Spinning machines conforming to this type may be formed as, for example, air jet spinning machines, which are used to produce a yarn from a strand-like fiber material (such as a fiber band) with the assistance of a vortex air flow generated by air nozzles within a vortex chamber. For this purpose, with the assistance of a delivery device, which is preferably formed by a pair of output rollers of a drafting system upstream of the spinning unit in the direction of spinning, a strand-like fiber material is conveyed in the direction of the spinning unit and is sucked or drawn in by it through negative pressure. The fiber material ultimately enters the interior of the spinning unit and there into the area of the inlet mouth of a spindle-shaped yarn formation element. The outer fibers of the strand-like fiber material are wound around the inner fibers with the assistance of the vortex air flow in the area of the inlet mouth generated by the air nozzles, such that the result is a stable yarn, which, with the assistance of a draw-off device arranged outside of the spinning unit, is ultimately drawn out through the draw-off channel from the vortex chamber, and is spooled on a tube by means of the winding device.
Likewise, the spinning machine in accordance with the invention may also be formed as a so-called rotor spinning machine, which is adequately described in the state of the art, the principle of which consists of the fact that the fibers of a likewise strand-shaped fiber material are separated with the assistance of an opening device (usually in the form of an opening roller) and are fed to the rapidly rotating rotor of the spinning unit. Based on the rotor speed, the individual fibers are laid at the inner wall of the rotor, and are thereby twisted into each other. The twisted fibers may ultimately be drawn out through an outlet of the spinning unit and spooled onto a sleeve of a downstream winding device.
If, during the spinning process, spinning errors (non-tolerable hairiness or thick or thin parts in the yarn, unsatisfactory supply of fiber material, etc.) arise, or if one or more spinning stations is turned off for a certain period of time, yarn production must be interrupted at the respective spinning station(s). This occurs, for example, by stopping the unit delivering the fiber material into the spinning unit (such as the drafting system of an air jet spinning machine) and/or the spinning unit itself. If yarn production is restarted after the stopping of yarn production and, in particular, after the removal of the faulty yarn section, a piecing process is necessary at the previously stopped spinning station.
Herein, the coil-side end of the already produced yarn (that is, the end section of the yarn section last spooled before the interruption of yarn production) is returned counter to the actual spinning direction, and possibly after one or more intermediate steps (for example, a yarn end preparation), through the outlet of the spinning unit, into or through it. Subsequently, the yarn end is brought into contact with the fiber material fed to the spinning unit or the correspondingly fed individual fibers, and is drawn off in the direction of spinning out of the spinning unit. Thereby, normal spinning operation is ultimately resumed, with which a yarn is produced from the fiber material fed to the spinning unit.
Generally, it then occurs again and again that a piecing process must be carried out at multiple spinning stations simultaneously (for example, during the start-up of the spinning machine, upon which a piecing has to be carried out at all of the spinning stations, or after the interruption of yarn production at multiple spinning stations). Herein, however, the problem arises that the spinning machine is usually designed to carry out a limited number of simultaneous piecing processes. If the piecing process is carried out or supported by, for example, by a service unit (a so-called “service robot”) that is movable back and forth along the spinning stations, the number of simultaneously piecing spinning stations is limited by the number of service units. Likewise, the number is limited if the piecing processes are carried out by piecing devices associated with the spinning stations, since these have a certain energy and in particular a certain need for compressed air or negative pressure, which can be covered by the spinning machine only up to a certain degree.
Thus, as a result, only a certain number of piecing processes can always be carried out simultaneously, whereas it is customary in the state of the art to execute the piecing processes at the spinning stations in the chronological sequence in which they were previously stopped. Even if this approach is quite simple to realize in terms of control technology, there is a need for improvement to reduce the total time required to carry out the piecing processes per hour of operation of the spinning machine.